1. Field of Invention
This invention relates to missile guidance systems. Specifically, the present invention relates systems for determining missile closing rate and relative range with respect to a target.
2. Description of the Related Art
Missiles are used in a variety of demanding applications ranging from explosives delivery to satellite launching applications. Such applications often require accurate target closing rate and closing distance information to make in-flight steering and arming adjustments.
Missile guidance algorithms depend on accurate closing distance, i.e., range, and closing rate information to accurately time the activation of missile arming procedures and to successfully direct a missile to its target. Poor or corrupted missile closing rate and/or range information may cause premature missile detonation or missile targeting error.
In active missile systems, a transmitter onboard the missile facilitates ranging, i.e., a determination of the distance between the missile and the target. By measuring the round trip signal travel time for a signal transmitted via the transmitter and reflected back from the target, a range estimate is obtained.
Semi-active systems utilize a stationary or semi-stationary transmitter or illumination source. Semi-active missile systems often rely on an initial estimate of the target position and in-flight kinematic measurements provided by an onboard missile accelerometer such as an inertial reference unit (IRU) to estimate range. These systems typically lack the ability to accurately determine range when a target is in motion. Range estimated in this way is often grossly inaccurate and can result in inefficient missile guidance, increased fuel consumption and miss-timed missile detonation. All of these characteristics tend to reduce missile effectiveness.
To facilitate the determination of missile position, missiles used in military applications often include an IRU for taking missile kinematic measurements. The IRU has a sensor that detects changes in missile inertia. The changes in inertia are then used to compute missile acceleration, velocity, and position. The current missile position and velocity are calculated with reference to an initial position and velocity, respectively. However, initialization error and IRU measurement error accumulate over the flight of a missile, severely degrading missile position and target closing rate estimates.
In semi-active missile systems that rely on IRU measurements, an initial range measurement is stored in an onboard missile guidance computer. Activation of arming procedures is determined via the initial range measurement. However, if a maneuvering target accelerates or decelerates after missile launch, error in the range information grows in direct proportion to the deceleration or acceleration. Error in the range information may result in premature missile detonation or targeting errors.
Hence, a need exists in the art for a system for facilitating accurate determination of missile range, that is immune to IRU initialization error, and that is applicable to semi-active missile systems. There is a further need for a system for facilitating accurate determination of range to a rapidly maneuvering or accelerating target.